This invention relates to telecommunications networks. More particularly, this invention relates to an improved network architecture for more effectively routing traffic and recovering from failures.
A telecommunications network transports information from a source to a destination. The source and destination may be in close proximity, such as in an office environment, or thousands of miles apart, such as in a long distance telephone system. The information, which may be, for example, computer data, voice transmissions, or video programming, is known as traffic, and enters a network usually at a node and is transported through the network via links and other nodes until a destination is reached. Nodes are devices or structures that direct traffic; they add new traffic to the network, drop traffic from the network, and route traffic from one portion of the network to another. Links are the transmission paths interconnecting the nodes.
Nodes range in complexity from simple switching or relay devices to entire buildings containing thousands of devices and controls. Nodes can be completely controlled by a central network controller or can be programmed with varying degrees of automated traffic-managing capabilities. The implementation of nodes, which is known in the art, is accomplished either electronically, mechanically, optically, or in combinations thereof.
Links are typically either coaxial cable or fiber-optic cable, but can be any transmission medium capable of transporting traffic. Individual links can vary in length from a few feet to hundreds of miles. Links that are part of a larger network, such as a telephone system, are usually carried on overhead utility poles, in underground conduits, or in combinations of both. Generally, links are either working links or protection links. Working links provide dedicated pathways for transporting traffic, while protection links, which do not regularly transport traffic, provide alternative pathways should a working link become inoperative. A link can become inoperative in a number of ways, but most often, when it is cut. This usually occurs, for example, when excavation severs an underground link, or when a traffic accident or storm damages a utility pole carrying a link.
The volume of traffic transported by a network can be significant. Typical transfer rates for a fiber-optic link can range from 2.5 gigabits per second to 10 gigabits per second. A xe2x80x9cgigabitxe2x80x9d is a billion bits, and a xe2x80x9cbitxe2x80x9d is a binary digit (a logical 1 or 0), which is the basic unit of digitized data. Digitized data is a coded sequence of bits, and traffic is typically transported in that form.
Because of the significant volume of traffic typically transported by a network, any disruption in traffic flow can be devastating. Of particular concern are telephone networks, which can transport thousands of individual communications simultaneously. Thus the ability to restore network service should a portion of the network become inoperative is of high priority. Moreover, to ensure that the network is implemented and managed in a cost effective manner, proper allocation of link resources is also of high priority.
Network architecture (the manner in which nodes and links are configured and traffic is controlled) plays a significant role in both the cost-effective implementation and management of a network and the ability of a network to quickly recover from traffic flow disruptions. In one known mesh network, a central controller monitors and controls traffic flow throughout the network. Complex traffic routing and recovery algorithms are used to manage traffic flow. A simplified portion of this network is shown in FIG. 1. Each node 102 communicates with controller 104, sending status and receiving instructions for properly routing traffic. Each node is interconnected with other nodes by working links 106 (indicated by solid lines) and selectively placed protection links 108 (indicated by dashed lines). (For clarity, not all nodes and links in FIG. 1 are identified with reference numerals.)
When a link becomes inoperative, the nodes connected to the inoperative link immediately notify the controller. The controller then determines if an alternative traffic path can be configured with either protection links, spare capacity on working links, or combinations of both. If an alternative path is found, the controller sends appropriate instructions to those nodes that can interconnect the identified links to form the alternative path. Typical recovery time from such a disruption is approximately two seconds. This recovery time was once hailed as a marvel of technology; today, however, it is no longer acceptable. A two-second outage would adversely affect, for example, the transmission of computer data. In fact, an entire computer center could be adversely affected by such an outage.
To improve recovery times, other known mesh networks provide decentralized node control. In these networks, individual nodes, in cooperation with adjacent nodes, routinely route traffic and respond to path failures without significant interaction with the central controller. By communicating locally among themselves, these nodes can, for example, recover from path failures by configuring alternative paths and rerouting traffic to those alternative paths. Decentralized node control has improved recovery times to the millisecond range (thousandths of a second).
Furthermore, restorative capability in these networks has been improved by providing each nodal interconnection with a protection link. This additional protection link coverage increases the likelihood that alternative paths can be configured for most typical path failures.
These improvements, however, have also resulted in several disadvantages. For example, decentralized node control undesirably requires a great deal of inter-nodal communication, which must be supported with increased link capacity and more complex nodes. Nodes must be able to send, receive, analyze, and respond to various inter-nodal traffic management communications, and working link capacity must be increased to transport those communications. Moreover, the additional protection link coverage further increases equipment and maintenance costs. Thus these improvements have undesirably resulted in a more costly network, both in terms of original equipment and the associated maintenance of that equipment.
Networks employing architectures other than mesh configurations are also known. Ring networks, for example, interconnect nodes in a circular fashion to form rings. The rings are then interconnected to form a complete network. Control in this type of network is also decentralized, enabling nodes within each ring to make limited traffic routing decisions. Although the rings are interconnected, each ring operates substantially independently of the others, thus desirably reducing the possibility of a network-wide failure, which a centrally controlled network is susceptible to. Ring networks have further improved recovery times to the microsecond range (millionths of a second). In that short amount of time, telephone customers would not realize that the path carrying their call was cut and rerouted, and transmitted computer data would likely suffer the loss of only a few hundred bits of data, which would simply require retransmission of the lost bits.
A portion of such a ring network is shown in FIG. 2A. Network 200 includes nodes 202, 204, 206, 208, and 210. Each node is connected to working links, indicated by solid lines (such as working link 212), and protection links, indicated by dashed lines (such as protection link 214). (For clarity, only the working and protection links of one link pair are identified with reference numerals in FIG. 2A.)
A ring recovers from a cut link pair generally as follows: assume the working and protection links between nodes 202 and 204 are cut. Nodes 202 and 204 communicate with adjacent nodes 210 and 206, respectively, which in turn both communicate with node 208 to switch disrupted traffic to the protection links. Traffic flow is thus restored between nodes 202 and 204 by rerouting disrupted traffic back around the ring through protection links.
A disadvantage of this ring network is that restoration is limited to substantially only one inoperative link pair per ring. If, for example, two link pairs were cut in the same ring, traffic flow could not be restored until at least one of the link pairs was physically repaired. This disadvantage is not shared by the previously described mesh network, because most nodes in a mesh network are usually connected to three or more other nodes, increasing the likelihood that a sufficient number of protection links can be configured to completely restore disrupted traffic flow.
A further disadvantage is the high percentage of links deployed for protectionxe2x80x94a full 50% around the entire ring. Moreover, the traffic-bearing capacity of the protection links is substantially the same as the working links. Thus, half the link capacity in the network either sits idle, or, at best, is underutilized with nonessential or low priority activity until needed to restore disrupted traffic flow. This high percentage of underutilized link capacity is undesirable in today""s competitive cost-conscious environment.
A still further disadvantage of this ring network is the susceptibility of complete inter-ring communication failure should the interconnecting node fail (i.e., node 210 in FIG. 2A). To guard against such failures, other known ring networks have been developed with DRI (Dual Ring Interworking). This ring architecture, shown in FIG. 2B, provides two copies of inter-ring traffic between each pair of rings. One copy is transported through each of redundant paths 252 and 254. Should there be an inter-link or inter-node failure, the network automatically uses the other copy of the transmitted inter-ring traffic. Unfortunately, however, this architecture undesirably requires additional link and node resources that accordingly reduce the cost effectiveness of the network.
In view of the foregoing, it would be desirable to provide a network architecture for a telecommunications network that more cost effectively provides high levels of traffic routing diversity and restorative capability.
It would also be desirable to provide a network architecture for a telecommunications network that provides decentralized node control requiring less inter-nodal communication.
It would further be desirable to provide a network architecture for a telecommunications network that offers high levels of restorative capability with protection links of less traffic-bearing capacity.
It would still further be desirable to provide a network architecture for a telecommunications network that operates with less complex traffic routing and recovery algorithms.
In accordance with the present invention, a network architecture is provided for configuring a telecommunications network into a plurality of n-dimensional hypercubes, the network having a plurality of nodes and a plurality of links, and xe2x80x9cnxe2x80x9d being an integer greater than or equal to three. Each hypercube is interconnected with at least one other hypercube and has 2n vertex nodes. Each vertex node has a degree n, meaning that it is connected with links to n other vertex nodes.
Additional features include decentralized node control, substantially independent traffic management within each hypercube, working and protection links with less traffic-bearing capacity, unique vertex node labeling that reduces inter-nodal communication, and less complex traffic routing and recovery algorithms.